Method for transurethral delivery of thermal therapy to tissue

ABSTRACT

An apparatus for applying thermal energy to a prostate gland, comprising a support tube having a longitudinal passageway, a power lead channeled through the longitudinal central passageway and an ultrasound crystal disposed around at least part of the support tube. The ultrasound crystal is coupled to the power lead which provides the power to energize the ultrasound crystal and generate ultrasound energy providing thermal therapy to the prostate gland. The ultrasound crystal further includes inactivated portions for reducing ultrasound energy directed to the rectal wall of the patient. A sealant is disposed in contact with the ultrasound crystal allowing vibration necessary for efficient ultrasound energy radiation for the thermal therapy of the prostate gland.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.10/397,070 filed on Mar. 24, 2003, now U.S. Pat. No. 8,025,688,incorporated herein by reference in its entirety, which is acontinuation of U.S. patent application Ser. No. 08/858,912 filed on May19, 1997, now U.S. Pat. No. 6,537,306, incorporated herein by referencein its entirety, which is a continuation of U.S. patent application Ser.No. 08/332,997 filed on Nov. 1, 1994, now U.S. Pat. No. 5,733,315,incorporated herein by reference in its entirety, which is acontinuation-in-part of U.S. patent application Ser. No. 08/291,336filed on Aug. 17, 1994, now abandoned, incorporated herein by referencein its entirety, which is a continuation-in-part of U.S. patentapplication Ser. No. 08/083,967, filed Jun. 25, 1993, now U.S. Pat. No.5,391,197, incorporated herein by reference in its entirety, which is acontinuation-in-part of U.S. patent application Ser. No. 07/976,232filed on Nov. 13, 1992, now abandoned, incorporated herein by referencein its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an apparatus and method forperforming a thermotherapy patient treatment protocol. Moreparticularly, the invention relates to a novel apparatus and method forheating the prostate gland for therapeutic purposes.

2. Description of Related Art

Thermotherapy treatment is a relatively new method of treating diseasedand/or undesirably enlarged human prostate tissues. Hyperthermiatreatment is well known in the art, involving the maintaining of atemperature between about 41.5° through 45° C. Thermotherapy, on theother hand, usually requires energy application to achieve a temperatureabove 45° C. for the purposes of coagulating the target tissue. Tissuecoagulation beneficially changes the density of the tissue. As thetissue shrinks, forms scars and is reabsorbed, the impingement of theenlarged tissues, such as an abnormal prostate, is substantiallylessened.

The higher temperatures required by thermotherapy require delivery oflarger amounts of energy to the target prostate tissues. At the sametime, it is important to shield nontarget tissues from the highthermotherapy temperatures used in the treatment. Providing safe andeffective thermotherapy, therefore, requires devices which have furthercapabilities compared to those which are suitable for hyperthermia.

Though devices and methods for treating benign prostatic hyperplasiahave evolved dramatically in recent years, significant improvements havenot occurred and such progress is badly needed. As recently as 1983,medical textbooks recommended surgery for removing impinging prostatictissues and four different surgical techniques were utilized. Suprapubicprostatectomy was a recommended method of removing the prostate tissuethrough an abdominal would. Significant blood loss and the concomitanthazards of any major surgical procedure were possible with thisapproach.

Perineal prostatectomy was an alternatively recommended surgicalprocedure which involved gland removal through an incision n theperineum. Infection, incontinence, impotence or rectal injury were morelikely with this method than with alternative surgical procedures.

Transurethral resection of the prostate gland has been anotherrecommended method of treating benign prostatic hyperplasia. This methodrequired inserting a rigid tube into the urethra. A loop of wireconnected with electrical current was rotated in the tube to removeshavings of the prostate at the bladder orifice. In this way, noincision was needed. However, strictures were more frequent and repeatoperations were sometimes necessary.

The other recommended surgical technique for treatment of benignprostatic hyperplasia was retropubic prostatectomy. This required alower abdominal incision through which the prostate gland was removed.Blood loss was more easily controlled with this method, but inflammationof the pubic bone was more likely.

With the above surgical techniques, the medical textbooks noted thevascularity of the hyperplastic prostate gland and the correspondingdangers of substantial blood loss and shock. Careful medical attentionwas necessary following these medical procedures.

The problems previously described led medical researchers to developalternative methods for treating benign pro static hyperplasia.Researchers began to incorporate heat sources in Foley catheters afterdiscovering that enlarged mammalian tissues responded favorably toincreased temperatures. Examples of devices directed to treatment ofprostate tissue include U.S. Pat. No. 4,662,383 (Harada). U.S. Pat. No.4,967,765 (Turner), U.S. Pat. No. 4,662,383 (Sogawa) and German PatentNo. DE 2407559 C3 (Dreyer). Though these references disclosed structurewhich embodied improvements over the surgical techniques, significantproblems still remained unsolved. Recent research has indicated thatenlarged prostate glands are most effectively treated with highertemperatures than previously thought. Complete utilization of thisdiscovery has been tempered by difficulties in shielding rectal walltissues and other nontarget tissues. While shielding has been addressedin some hyperthermia prior art devices, the higher energy fieldintensities associated with thermotherapy necessitate structures havingfurther capabilities beyond those suitable for hyperthermia. Forexample, the symmetrical microwave-based devices disclosed in theabove-referenced patents have generally produced relatively uniformcylindrical energy fields. Even at the lower energy field intensitiesencountered in hyperthermia treatment, unacceptably high rectal walltemperatures have limited treatment periods and effectiveness. Furtherwhile shielding using radioreflective fluids has been disclosed in theprior art (see for example European Patent Application No. 89,403,199)the location of such radioreflective fluid appears to increase energyfield intensity at the bladder and rectal wall. This is contrary to oneof the objects of the present invention.

In addition, efficient and selective cooling of the devices is rarelyprovided. This increases patient discomfort and increases the likelihoodof healthy tissue damage. These problems have necessitated complex andexpensive temperature monitoring systems along the urethral wall.

Finally, the symmetrical designs of the above-referenced devices do notallow matching of the energy field to the shape of the abnormallyenlarged prostate gland. Ideally, the energy field reaching the tissuesshould be asymmetric and generally should expose the upper and lateral(side) impinging lobes of the prostate gland to the highest energy. Inaddition, the field is ideally substantially elliptical such that theenergy reaching the sphincters is minimized.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an improvedapparatus and method suitable for ultrasound treatment of tissue.

It is a further object of the invention to provide an improved apparatusand method for thermotherapy treatment which provides a smaller probewith higher ultrasound energy output on target tissues.

It is yet a further object of the invention to provide a novel methodand apparatus having high ultrasound energy output on target tissueswhile producing substantially no energy output directed to nontargettissues.

It is yet another object of the invention to provide an improvedapplicator designed to be inserted into an orifice of a male patient,wherein the applicator includes a small diameter ultrasound probe.

It is a still further object of the invention to provide a novel meansfor dynamic monitoring of the treatment temperature distribution and touse such information to aid in the control of the deposited power leveland its distribution.

It is another object of the invention to provide and improved ultrasonicapplicator which can be inserted into the urethra and can be positionedwith respect to the prostate and maintained in position duringtreatment.

It is a further object of the invention to provide an improved methodand apparatus using ultrasound energy for the treatment of prostatedisease and, more particularly to provide an ultrasound applicatorconsisting of multiple transducers which can be inserted into theurethra or rectum and direct the energy in such a manner as toselectively treat the prostate gland.

It is yet another object of the invention to provide a novel method andapparatus utilizing ultrasound energy to achieve therapeutictemperatures in the prostate with better control of power depositionspatially within the prostate gland than is possible with prior artdevices.

It is an additional object of the invention to provide an array ofultrasound transducers producing an energy field having a gap or “deadzone” whereby tissues (such as the rectum, the distal sphincter and theverumontanum) are protected from energy transmission.

It is a further object of the invention to provide improved control ofboth the ultrasonic power level and the distribution of the powerdeposited in the prostate in a dynamic fashion which compensates forphysiological changes (temperature, blood flow effects) that can occurduring therapy and accommodates operator-desired alterations in thetherapeutic energy distribution within the prostate

It is another object of the invention to provide an improvedthermotherapy device which includes a collimated irradiation of a targetzone generally and selective cooling of nontarget tissues.

It is still an additional object of the invention to provide an improvedthermotherapy device which reduces tissue damage and discomfort byproviding more effective cooling to nontarget tissues.

It is an additional object of the invention to provide an improvedthermotherapy apparatus having one or more extended, and nondistensiblebut expandable balloons.

It is an additional object of the invention to provide an improvedthermotherapy device which includes ultrasound transducers or otherenergy sources capable of producing a substantially asymmetric energyoutput field, thus minimizing energy reaching the rectal wall in benignpro static hyperplasia thermotherapy treatment.

It is still a further object of the invention to provide an improvedthermotherapy apparatus which produces an energy field shaped inaccordance with the enlarged mammalian gland to be treated.

Other advantages and features of the invention, together with theorganization and manner of operation thereof, will become apparent fromthe following detailed description when taken in conjunction with theaccompanying drawings, wherein like elements have like numeralsthroughout the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 illustrates a schematic view of a thermotherapy deviceconstructed in accordance with one form of the invention;

FIG. 2 shows an isometric view of an ultrasound crystal having a portionof its electrode coating removed;

FIG. 3 illustrates an end view of the ultrasound crystal constructed inaccordance with the invention and shown in FIG. 2;

FIG. 4 shows an isometric view of an ultrasound crystal including twoscore lines creating a region rendered incapable of radiating ultrasoundenergy;

FIG. 5 shows a top view of the template implant for in vivo thermometryplacement with respect to the applicator for thermal dosimetrymeasurements;

FIG. 6 illustrates a front view of the template implant for in vivothermometry placement with respect to the applicator for thermaldosimetry measurements;

FIG. 7 illustrates simulated temperature profiles from a 2.5 mm diameterultrasound applicator within a 6 mm diameter water-cooled deliverycatheter with T_(c) equal to 20° C.;

FIG. 8 illustrates acoustic output power levels as a function ofelectrical input power for four individual tubular array transducersdriven at peak resonant frequency;

FIGS. 9A-9D show longitudinal temperature profiles measured in pig thighmuscle at A) 0.5 cm; B) 1 cm; C) 2.0 cm; and D) 3.0 cm radial depths;

FIG. 10 illustrates tangential temperature profiles measured in the pigthigh muscle across the central heating zone;

FIGS. 11A-11E illustrate angular temperature profiles at a) Probe #1,0.5 cm depth; b) Probe #2, 2 cm depth; c) Probe #3, 1.0 cm; d) Probe #4,3.0 cm and e) Probe #5, 1.0 cm;

FIGS. 12A-12E show a different plot format of angular temperature at a)Probe #1, 0.5 cm depth; b) Probe #2, 2 cm depth; c) Probe #3, 1.0 cm; d)Probe #4, 3.0 cm and e) Probe #5, 1.0 cm;

FIGS. 13A-13D illustrate radial temperature profiles in the pig thighmuscle after ten minutes of therapy for low power tests (FIGS. 13A and13C) and high power tests (FIGS. 13B and 13D);

FIG. 14 shows a front view of an ultrasound applicator constructed inaccordance with one form of the invention;

FIG. 15A illustrates an end view of an ultrasound crystal useful in oneform of the intervention; and

FIG. 15B shows a front view of the crystal shown in FIG. 15A.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures and more particularly to FIG. 1, athermotherapy device constructed in accordance with the invention isindicated generally at 10. Throughout the application when referring to“thermotherapy,” this terminology shall be meant to include boththermotherapy treatment as well as hyperthermia treatment unlessspecifically stated to exclude one therapy.

The thermotherapy device includes a delivery system 12 which is coupledto the degassed and temperature regulated water flow 14 as well as RFamplifiers 16 and more fully described in U.S. patent application Ser.No. 08/083,967. While five tubular ultrasound transducers 18 are shownfor non-limiting, illustrative purposes, it will be apparent to oneskilled in the art that the number and configuration of ultrasoundtransducers can be varied depending on the particular applicationinvolved.

The delivery system can take a number of forms, though preferably adelivery system such as the one described in U.S. patent applicationSer. No. 07/976,232 is used. The critical parameters of the deliverysystem 12 include the ability to provide degassed and temperaturerelated water flow into the delivery system adjacent prostate tissue tobe treated, as well as enabling individual control of each of theultrasound transducers 18.

The ultrasound transducers 18 are preferably substantially cylindricalin shape. Conventional transducers 18 having this shape radiate asubstantially symmetrical energy field. This has been found to beundesirable in prostate treatment as explained in detail in U.S. patentapplication Ser. No. 08/083,967. As described therein, the primaryproblem with a symmetrical energy field is heating of the rectal wallduring prostate treatment. Irreversible damage to the rectal wall canresult from such an energy field if power levels are sufficient toeffectively treat areas of the prostate. Accordingly, the ultrasoundtransducers 18 are modified in accordance with one form of theinvention.

The ultrasound transducers 18 are modified to create a portion incapableof producing virtually any ultrasound energy. This can be accomplishedin one of two ways in accordance with this form of the invention. Thefirst method (as shown in FIGS. 2 and 3) involves removing the electrodecoating 20 from a portion of the ultrasound crystal 22. As used herein,the term “ultrasound crystal” shall refer to the nickel-plated piezoceramic structure which is unconnected to a housing 24, power leads 26or the RF amplifiers 16. The term “ultrasound transducer; shall refer tothe ultrasound crystal 22 coupled to power leads 26 and mounted on ahousing 24. Removing part of the electrode coating 20 as shown in FIGS.2 and 3 provides a means for protecting the rectal wall of the patentfrom undesirably heating by shaping the energy field. This enablesenergy levels, and therefore the heating temperatures of the prostate,to be increased for more effective thermal therapy.

An alternative way of producing a portion which is substantiallyincapable of producing ultrasound energy is to score the electrodeportion 21 of the ultrasound crystal 22. While the depth of the scorelines 25 can be varied, preferably the scoring extends to a depth of40-50% of the depth of the ultrasound crystal 22 exterior. The scoringcan be accomplished using conventional cutting tools such as a diamondsaw.

While a variety of ultrasound transducer housings 24 and deliverysystems 12 can be used, preferably a delivery system 12 produced byDornier Medical Systems, Inc. and sold commercially is used. Thedelivery system 12 can be reamed out to fit the size of ultrasoundtransducer housing assembly 30 as desired.

The ultrasound transducer housing assembly 30 can comprise a widevariety of configurations. Preferably, the assembly 30 is produced byproducing apertures 31 in a thin walled tube 32, through which the powerleads 34 for the ultrasound crystal 22 are run as shown in FIG. 14. Thethin walled tube 32 can comprise a variety of biocompatible,noncorrosive materials, although preferably No. 304 stainless steel(thin needles stock) is used. The wires are run through the apertures31, and an ultrasound crystal 22 is slid over the power leads 34, andsoldered thereto. Any number of crystals 22 can be mounted this way,depending on the length of the thin wall tube 32 and the applicationdesired. Next, silicone sealant 38 such as that sold commercially byGeneral Electric as Silicon II Glue Seal and Gasket is deposited betweenthe ultrasound crystals 22 and over the thin walled tube 32. Thesilicone sealant 38 acts as an adhesive, but allows the vibrationnecessary for efficient ultrasound energy radiation. The siliconesealant 38 also provides a water tight seal. While the assembly could beused in this form, preferably the assembly 30 is covered withshrink-wrap material 40 such as “SPIROBOUND” heat-shrink tubing whichshrinks when exposed to heat. The shrink-wrap is exposed to aconventional heat source such as a propane torch in a controlled manner,and one obtains even shrinkage and a good seal by technique such asrotating the assembly 30 while heating. The resulting assembly is robustand highly efficient.

While a variety of ultrasound crystals 22 can be used, preferably theultrasound crystal 22 shown in FIGS. 15A and 15B is used. For additionaltransducer details, please see FIGS. 14A and 14B. This ultrasoundcrystal 22 is preferably provided by Stavely Sensors, Inc. of EastHartford, Conn. Or Valpey-Fischer Corp of Hopkinton, Mass., and producesextremely high power output for a small sized transducer.

EXAMPLE

In accordance with this form of the invention, a transurethralmultielement ultrasound applicator was used as a means of improvingheating penetration, spatial localization, and dynamic control to affordbetter treatments for cancer and BPH. This structure providedlongitudinal control of heating to cover the anterior-lateral portion ofthe prostate while sparing the region around the rectum andverumontanum. Computer simulations, acoustic measurements, and in vivothermal dosimetry studies confirmed the usefulness of this form of theinvention.

For a nonlimiting, illustrative example, prototype applicators werefabricated with four tubular transducer elements (each 6 mm long, 2.5 mmOD) attached to form a segmented array. Separation between elements wasapproximately 0.5 mm. Each transducer was modified to produce uniformcoverage of the anterior and lateral portions of the prostate and toensure that no acoustic energy would be delivered to the rectum duringclinical use. The multielement applicator was designed to be insertedwithin a modified catheter delivery system previously developed formicrowave BPH therapy (Dornier Medical Systems, Inc.), with annularcounter-current flow for water coupling of the acoustic energy andtemperature regulation of the catheter/urethra interface. (The coolingprovided by the delivery system protects the urethra). The heatingperformance of these ultrasound applicator was evaluated using computersimulation programs to calculate the acoustic fields and correspondingthermal distributions in tissue. The power deposition (<q>) of thesecylindrical sources in tissue can be approximated by the followingexpression:

$\begin{matrix}{{\langle q\rangle} = {\frac{2\alpha \; I_{o}{fr}_{o}}{r}^{{- 2}{\alpha/{({r - r_{o}})}}}}} & (1)\end{matrix}$

where I_(o) is the intensity at the transducer surface, r_(o) is theradius of the transducer, r is the radial distance from the center ofthe transducer, α is the amplitude attenuation coefficient, and f is thefrequency (MHz).

The temperature distributions resulting from the compiled powerdisposition patterns were calculated using the bio-heat transferequation (BHTE), a descriptive model of tissue thermal characteristics:

∇2(kT)−αbcb(T−Ta)+<q>=0  (2)

where k is the tissue thermal conductivity, w is the blood perfusionrate, c_(b) is the specific heat of tissue, T is the tissue temperatureand T_(a) is the arterial blood temperature. The steady-state solutionto this equation was computed using the finite difference technique withsuccessive over-relaxation. Typical values used were: α=5 Np m⁻¹ MHz⁻¹,k=0.528 W m⁻¹ °C.⁻¹, w=1-10 kg m⁻³ s⁻¹, c=3680 J kg⁻¹ °C.⁻¹, p=1000 kgm⁻³. A perfusion of w=2.0 kg m⁻³ s⁻¹ represents a moderately perfusedtissue (resting muscle); most tumors range from 0.1-5.0 kg m⁻³ s⁻¹.These simulations were configured to accurately model the presence ofapplicator water cooling of the applicator/tissue interface. Theacoustic force-balance technique adapted for cylindrical radiators wasused to measure the acoustic output power from these tubular transducersas a function of drive frequency and applied electrical power.

A 100 lb female farm pig was anesthetized using 1.5% Isoflourane and 0.61/min 02. A 0.5 inch thick Plexiglas template was used to ensurealignment of the thermometry probe tracks with the catheter deliverysystem (see FIGS. 5 and 6 for set up). 20 g. needles were insertedthrough the template for thermometry tracks at radial distances of 0.5to 3.0 cm from the catheter wall but aligned with the axis of thedelivery system. A tangential thermometry track was inserted orthogonalto the axis of the delivery system, 5 cm deep within the thigh, andglancing the surface of the catheter delivery system. Multijunctionthermocouple probes were inserted within the needles and moved in 0.5 cmincrements to obtain temperature maps along the length of theapplicator. The approximate radial depth of sensed needles from theouter surface of the delivery catheter was 0.5, 1.0, 2.0 and 3.0 cm.

A multichannel RF amplifier system was used to power each transducerwithin the applicator. The frequency sweep on center frequency for eachtransducer was adjusted to produce a uniform pressure disturbance asvisualized on the surface of water. A flow rate of 220 ml/min of 35° C.degassed water was maintained to the delivery system for the duration ofthe experiment.

The applicator was aligned within the catheter so that the “dead zone”aimed at #6 (probe track 6) and the central heating zone was aimed at#3. 2 watts of RF power was applied to each transducer element of theapplicator until a pseudo steady-state was achieved after 5 minutes.Temperature maps were obtained for all thermometry probes, and then thepower was turned off. The applicator was then rotated counter clockwiseby 30° within the delivery system. After the tissue cooled back toequilibrium (10-20 min) the process was repeated. This sequence wasrepeated until the pseudo-steady-state temperature profiles weremeasured for each thermometry tract as the applicator was rotated in 30°increments for a total of 180°.

Simulated radial temperature profiles (see FIG. 7) illustrated thateffective heating is possible to 2 cm depth with concurrent cooling toprotect the urethral mucosa (T_(c)=20° C., 7 MHz ultrasound). Theseexperimental results (see FIG. 9) demonstrate the distinct advantage ofmultielement ultrasound applicators over other techniques: the powerdeposition along the applicator length can be adjusted to produce moredesirable (elongated) temperature distributions such as adjustingheating length and accommodating dynamic changes in blood perfusion andtissue heterogeneity.

The acoustic efficiencies of these cylindrical ultrasound transducerswas between 55-60% at the peak resonant frequency. These efficienciesare high for such very small crystals. FIG. 8 demonstrates that acousticpower levels of almost 12 w per transducer are attainable with thisapplicator design.

The temperature distributions produced by this applicator in pig thighmuscle were measured using low temperature repetitive heating trials.(This was necessary to ensure repeatability between heating sessions andto avoid thermal damage to the tissue). The longitudinal temperatureprofiles at varying radial depths from the applicator surface are shownin FIGS. 9A-E, demonstrating that within the central heating zone thetherapeutic region extends towards the ends of the applicator and isfairly uniform, while isolated from the “rectal” region. The tangentialprofiles (FIG. 10) measured across the central heating zone illustrate aradial extension of the heated region 2-3 cm diameter. From a series ofmeasurements at different rotational angles, the steady-state peak(longitudinal) temperature rise as a function of applicator rotationalangle at varying depths are shown in FIGS. 11A-E, illustrating thepreferential localization of the heating to the anterior and lateralregions while protecting the rectum (located at zero degrees on theplots). Further data relating to temperature rise as a function ofalignment angle and longitudinal distance along the application areplotted in FIGS. 12A-E.

Finally, the applicator was repositioned to the initial startuporientation, and 8-10 acoustic watts of power was applied to eachtransducer in order to thermally ablate the “target” region an pseudosteady state temperatures were obtained. The radial temperaturedistribution achieved during the ablative sequence is shown in FIG. 12.

These results verified the usefulness of using the transurethralultrasound applicator of present invention for thermal therapy of theprostate. Theses applicators, inserted within a water-cooleddelivery-catheter, can produce heated regions extending more than 2 cmin radial depth, while sparing the urethral mucosa. A significantadvantage of multi-transducer ultrasound applicators is that thelongitudinal power deposition (heating pattern) can be dynamicallyaltered in response to tissue heterogeneities, thermally induced changesin blood perfusion, and to tailor the size of the treated region. Inaddition, the beam distributions from these applicators can be shaped inorder to produce desired circumferential or angular heating patternswhich can protect the rectal mucosa while localizing the energydeposition to the anterior and lateral sections. This is a significantimprovement over previous designs using single antenna microwave energysources, which produce more elliptical or “football shaped”distributions which can not be adjusted. The in vivo thermal dosimetryexperiments also show that therapeutic temperatures in excess of 80° C.can be obtained with the present invention.

While preferred embodiments have been illustrated and described, itshould be understood that changes and modifications can be made thereinwithout departing from the invention in its broad aspects. Variousfeature of the invention are defined in the following claims.

1. A method for applying thermal therapy to a prostate gland of apatient, the method comprising: inserting an ultrasound applicatorwithin the urethra adjacent to a tissue target region in the patient;delivering power to the ultrasound applicator to generate ultrasoundenergy; and directing the ultrasound energy to selectively treat aregion of the prostate gland.
 2. A method as recited in claim 1, whereindirecting the ultrasound energy comprises shaping a distribution patternof the ultrasound energy to produce an angular treatment pattern.
 3. Amethod as recited in claim 2, wherein the pattern is shaped to localizethe ultrasound energy to an anterior and lateral region in the patient'stissue.
 4. A method as recited in claim 2, wherein the pattern is shapedto protect a region of rectal mucosa.
 5. A method as recited in claim 4,wherein selectively treating a region of the prostate gland comprisesheating sub-mucosal layers of urethral tissue while avoiding damage tothe mucosal layer.
 6. A method as recited in claim 5, wherein thepattern is shaped to avoid heating a region of rectal mucosa.
 7. Amethod as in recited claim 1, further comprising controlling theultrasound energy pattern to control the extent of a longitudinal energydistribution.
 8. A method as in recited claim 7, further comprisingdynamically altering the longitudinal energy distribution.
 9. A methodas recited in claim 8, wherein the energy pattern is dynamically alteredin response to one or more of the following: tissue heterogeneities;thermally induced changes in blood perfusion; or to tailor the size ofthe treatment region.
 10. A method as recited in claim 1, whereininserting an ultrasound catheter comprises transurethral delivery of theultrasound applicator.
 11. A method as recited in claim 1, furthercomprising delivering a cooling fluid to the ultrasound applicator toselectively cool a non-target region of the patient.
 12. A method asrecited in claim 1, further comprising: measuring the tissue temperatureduring treatment; and adjusting the delivery of ultrasound energy inresponse to the tissue temperature measurement.
 13. A method fortransurethral delivery of thermal therapy to a prostate gland of apatient, the method comprising: inserting an ultrasound applicatorwithin the urethra adjacent to a tissue target region in the patient;delivering power to the ultrasound transducer to generate ultrasoundenergy; and directing the ultrasound energy to selectively treat aregion of the prostate gland.
 14. A method as recited in claim 13,wherein directing the ultrasound energy comprises shaping an ultrasoundenergy distribution pattern generated by the ultrasound transducer toproduce an angular treatment pattern.
 15. A method as recited in claim13, wherein the ultrasound applicator further comprises an outer coversurrounding the ultrasound transducer, the method further comprisingdelivering a cooling fluid to the ultrasound applicator, the fluiddisposed between the ultrasound transducer and the outer cover, whereinthe fluid selectively cools a non-target region of the patient.
 16. Amethod as recited in claim 13, wherein directing the ultrasound energycomprises translating the ultrasound applicator within the tissue targetregion of the patient to selectively treat a region of the prostategland.
 17. A method as recited in claim 13, wherein directing theultrasound energy comprises rotating the ultrasound applicator withinthe tissue target region of the patient to selectively treat a region ofthe prostate gland.
 18. A method for transurethral delivery of thermaltherapy to a prostate gland of a patient, the method comprising:inserting an ultrasound applicator within the urethra adjacent to atissue target region in the patient, the ultrasound applicatorcomprising a support member and a plurality of spaced-apart ultrasoundtransducers coupled thereof; delivering power to the ultrasoundtransducers to generate ultrasound energy; and directing the ultrasoundenergy to selectively treat a region of the prostate gland.
 19. A methodas recited in claim 18, wherein delivering power to the ultrasoundtransducers comprises delivering power to individual transducers, andwherein directing the ultrasound energy comprises controlling anultrasound energy distribution pattern to control the extent oflongitudinal energy distribution.
 20. A method as recited in clam 19,wherein the extent of longitudinal energy distribution is dynamicallyaltered in response to one or more of the following: tissueheterogeneities; thermally induced changes in blood perfusion; or totailor the size of the treatment region.
 21. A method as recited inclaim 18, wherein the ultrasound applicator further comprises an outercover surrounding the ultrasound transducers, the method furthercomprising delivering a cooling fluid to the ultrasound applicator, thefluid disposed between the ultrasound transducers and the outer cover,wherein the fluid selectively cools a non-target region of the patient.